The present invention is generally directed to inks, and more specifically, thermal ink jet inks and processes thereof. In embodiments, the present invention is directed to inks obtained by the addition of oil soluble dyes, especially highly, about 20 to about 60 weight percent loading soluble dyes to colored, like pigmented polymer particles, especially the sulfopolyester resins indicated in the appropriate patents and copending applications recited herein, to form ink jet inks with water and wherein the optical density thereof is improved, especially on paper and transparencies. More specifically, the present invention relates to inks obtained by the incorporation therein of an effective small amount, for example about 0.05 to about 5 weight percent, of an oil soluble dye, and which inks possess excellent waterfastness, superior smear resistance, and high optical densities of, for example, from about 1.4 to about 1.6 as measured using a MacBeth or X-Rit densitometer compared to similar inks without such dyes wherein the optical density thereof is from about 1.2 to about 1.3. The present invention in embodiments thereof enables the utilization of polymers obtained by polycondensation reactions, such as polyesters, and more specifically, the sulfonated polyesters as illustrated in U.S. Pat. No. 5,348,832, and U.S. Patent No. 5,604,076, the disclosures of which are totally incorporated herein by reference.
Main advantages associated with the inks of the present invention are the selection of pigmented inks with excellent lightfastness; the use of oil soluble dyes which enables the design of inks with improved color saturation; the use of oil soluble dyes which permits more ink design latitude since for example, a lower concentration of colorants, such as pigments can be used by also employing known dyes as colorants, and the oil dye also allows inks with a superior color gamut and higher color saturation.
The following characteristics are generally desired for inks utilized in ink jet printing processes:
(1) the ink should possess liquid properties, such as viscosity, surface tension and electric conductivity, corresponding to the discharging conditions of the printing apparatus, such as the driving voltage and driving frequency of the piezoelectric electric oscillator; PA1 (2) the ink should be capable of being stored for extended time periods without causing clogging of printhead orifices during use; PA1 (3) the ink should be quickly fixable onto a recording media, such as paper, film, and the like, such that the outlines of the resulting ink dots are smooth and there is minimal blotting of the dotted ink; PA1 (4) the resultant ink image should be of high quality, such as having a clear color tone and high density. The ink image should also possess high gloss and high color gamut and more importantly high optical density; PA1 (5) the resultant ink image should exhibit excellent waterfastness (water resistance) and lightfastness (light resistance); PA1 (6) the ink should not substantially chemically attack, corrode or erode surrounding materials, such as the ink storage container, printhead components, orifices, and the like; PA1 (7) the ink should not have an unpleasant odor and should not be toxic or inflammable; and/or PA1 (8) the ink should exhibit low foaming and high pH stability characteristics.